AN airliner carrying 180 passengers over Scotland came within just 300ft of colliding with a UFO, an official probe has revealed.

The unidentified flying object – described by the flight crew as “blue, yellow and silver” – loomed ahead of the Airbus A320.

Then it flew underneath the jet before the pilot had any time to react.

Both the plane’s pilots reported seeing the object 300ft ahead when the aircraft was on its final approach to Glasgow Airport.

One immediately told air traffic control: “Not quite sure what it was but it’s definitely quite large and it’s blue and yellow.”

He filed a report when he touched down at Glasgow and said the collision risk was high.

The investigation has ruled out the presence of any aircraft or stray weather balloons, adding to the mystery.

The incident is recorded in an official report by the UK Airprox Board, who probe near-misses.

While air traffic control said they could see nothing else in the area at the time of the incident, the control centre at Prestwick did detect an “unidentified track history” 1.3 nautical miles east of the A320’s position 28 seconds earlier.

The traffic collision avoidance system on the plane detected nothing.

Last night, UK Airprox confirmed that the pilots had reported the object about 3500ft above Baillieston – 13 miles east of Glasgow Airport.

They said they could not name the airline because “anonimity encourages a robust reporting culture of such events”.

The jet was descending in clear conditions with the sun behind it last December 2, when both the pilot and the non-flying plot saw “an object ‘loom ahead’ at a range of about 100m,” the report said.

It added: “The object passed directly beneath before the crew had time to take avoiding action or had ‘really registered it’.

“They were both agreed that it appeared blue and yellow (or silver) in colour with a small frontal area but that it was ‘bigger than a balloon’.

“The controller stated that he was not talking to anyone else in that area and that nothing was seen on radar.

“A further detailed review of individual radar sources did not yield any conclusive radar data that matched the A320 pilot’s description of the encounter.

“The Air Traffic Control unit’s own radar replay also showed no surveillance traces in the immediate vicinity of the A320 at the time.”

On the ground, the A320 pilot gave a further description to the Glasgow aerodrome controller.

He said: “We seemed to only miss it by a couple of hundred feet – it went directly beneath us.

“Wherever we were when we called it in it was within about 10 seconds. Couldn’t tell what direction it was going but it went right underneath us.”

Asked if he thought it was a glider, the pilot replied: “Well, maybe a microlight – it just looked too big for a balloon.”

But the baffled board ruled a fixed-wing aircraft or helicopter was unlikely, as were a weather balloon or a glider, which were unlikely to be operating in the area. A hang-glider, para-motor, para-glider or parascender were also ruled out.

The report said: “Members were unable to reach a conclusion as to a likely candidate for the conflicting aircraft and it was therefore felt that the Board had insufficient information to determine a cause or risk.”

Aviation expert David Learmount said: “Sometimes airplanes do get too close to each other and if we don’t know how often it happens and under what circumstances, we can’t reduce risk in future.”